The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Continuous media recording systems write data to a disk in a continuous pattern. Prior to a write operation, servo sector information (e.g., preamble data, synchronization markers, and positioning information) is read from the disk. The servo sector information is used to position a read/write head and to correct head positioning error. Subsequent to correcting head positioning error, data is written to sectors of the disk at a desired position. When data is written to the disk in a continuous pattern, the data may be written generally at any point within a sector of the disk.
Bit-patterned media (BPM) recording systems provide increased storage capacity over continuous media recording systems. For example, BPM recording systems may store ten times more information on a magnetic storage device (e.g., a magnetic disk or hard disk) than continuous media recording systems. As an example, a BPM recording system may store 1 or more terabits (Tbit) of data in one square inch (in2) of a magnetic storage device.
BPM recording systems write data to a disk in discontinuous island-based patterns. Bits of data are stored at specific points or discrete bit islands on the disk. For example, each bit island may store 1 bit of data. Head positioning accuracy requirements of BPM recording systems are more stringent than those of continuous media recording systems. This assures that data is written over bit island areas of the disk while minimizing and/or avoiding attempts to write data over areas between bit islands.
A BPM recording system may include both a servo clock and a write clock. The servo clock may be used for timing read events of servo sector information from the disk. The write clock may be used for timing write events including data write or switching timing of a write head. Synchronization of the write clock with the patterned media is needed in a BPM recording system due to the discontinuous format of BPM. A write clock signal is synchronized when rising and/or falling edges of the write clock signal are aligned with start and end positions of the bit islands, such that writing occurs over the bit islands and not over areas between bit islands.
In a continuous media recording system, head positioning error is corrected prior to writing to a disk. A continuous media recording system may include a servo clock and a write clock. The servo clock is used for timing read events of servo sector information. The write clock is used for timing write events. Positioning of bits on the disk is defined by the positioning of the write head during the write process. A first order or second order phase lock loop (PLL) may be used to control and correct the frequency of the servo clock. The frequency of the write clock may be adjusted using open loop control by mirroring the corrections to the servo clock. The mirrored corrections may include frequency and phase adjustments.
A BPM recording system may also include a servo clock and a write clock. Timing requirements of (head) positioning are more stringent in BPM recording systems than continuous media recording systems due to the discontinuous island-based patterns (or separations between bit islands). Deviation in frequency and phase of a write clock can cause misalignment between write clock pulses and bit islands. A write clock signal is aligned with bit islands when rising and/or falling edges of the write clock signal are synchronized with starting edge and ending edge positions of the bit islands. A read/write head is synchronized with bit islands when the read/write head is positioned over a starting edge of a bit island and begins writing at the starting edge when a rising edge of a write clock signal occurs. Write clock synchronization and/or write head synchronization with bit islands prevents writing attempts over areas between bit islands. The areas between the bit islands may be non-magnetic areas or grooves (i.e. the bit islands may be separated by non-magnetic materials).
In a BPM recording system, write clock/bit island misalignment and/or loss in write clock synchronization can lead to writing errors. The writing errors can be difficult to detect and/or correct.